Ni-cr-mn alloys



Patented Feb. 17, 1953 UNITED STATES PATENT 'DFFICE I NI-CR-MN ALLOYS Jenn H. Jackson and Charles T; Greeifiiig, ei lumbus', Ohio, assignors, by ni'sne assignments; to The C. O. Jelliff Mfg. Corporation, South port, Conn.', a corporation N6 firming.

6 claims. (01. r 1r1 This invention relates to electrical resistor alloys and more particularly to alloys wherein high, electrical resistivity properties are combined with good physical properties.

It is, therefore, an objector this inventionto provide an alloy for preparing electrical resistors, sai'd alloy havingspecial electrical properties such :as high electrical resistivity, low thermal E. M. F. .againstco'pper, and a low temperature coefficient of'elect'rical resistivity, together with good physical properties such as high tensile strength and good workability.

Further objects and advantages of the present invention will be apparent in view .of the following detailed disclosure and description thereof.

Ingeneral, this invention relates to Ni-Cr-Mn alloys for electricalresistors and to methods of producing such alloys.

It has been found that alloys having compo- ;sitionsjdefined by the ranges 501% to 70% Ni, 8% to 28% (-Jr, and 15%, to 36%1Yin possess all the required and ,previously enumerated desirable properties of electrical resistonalloys. Preferred .compositions in the range 55-7 to 65% Ni, 8%

to 20% Cr, and 25% to 33% 'Mn possess these properties to, a marked degree.

size, and then ,wire'drawn. It has been found,

as part of this invention, that the electrical resistivity of wire so produced may be greatly improved by subjecting it to a heat treatment consisting of a solution treatment followed by an aging treatment at from about 600 F. to about 1200 F. for a period of from to 100 hours. Results of this treatment show that preferred aging teinperaturesare fromabout 850 F. to about 950 F. fora period, of from 1 to 5 hours. The treatmentabove described produces an'alloy or increased electrical resistivity with only a slight, acceptable embrittlement and asmall, immaterial lo ss in ductility. In the aging treatment, the exact holding-time will, of course, vary with-the alloy composition, but preferred holding times can readily be determined experimentally for a particular alloy by preparing a plot of electrical resistivity as a function of time at holding temperature. Whenthis is done, it will be found that as the holding time is increased the rate o immerse .iere ettr calr sist v y comes less, andthe curve tends to flatten out.

By selecting an aging time earn in this flatten in'g-ofl section one "can obtain a ductile Wire having an electrical J resistivity only slightly lower than the maximum obtainable. Prolonged aging times would obviously produce slightly higher electrical resistivityvalues, but would also biingabo'ut undesirame embrittlement.

The solution treatment of the Ni-Cr-Mn alloys may be carried out at temperatures in the 1500" F. to 2100 F. range; with preferred temperatures in the 1700" F.- to -210 0 F. range. As the temperature of solution treatment is increased from-1500 F. to 2100 F the time required is reduced from about hours to about 2 seconds where the wire is small and where it has undergone some previous working and where annealing is used. Solution-treating time must be increased i'f material is treated in cast form, or if the material has been previously aged to cause excessive precipitation. It is necessary that the solution treatment be followed by reasonably rapid cooling. hir'c'ooling is sufficient for: fine wire although Water quenchingis preferred for wire of -inch diameter or larger. These times may be sharply reduced to a few seconds by solution-treating the wire before making a few final light wire-drawing passes and then repeating the solutiontre'atment.

A particular type of 's'dlu-tion-treatment, -desig' nated as strand-annealingis especially effective as a preliminary step in the treatment of resistor alloys to improve their resistivity properties.

This strand-annealing step consists of passing the alloy through a' long furnace after the alloy has been drawn as a fine wire size. This is done, preferably, by passing the wire through the furnace at such a rate that it is inthe heating zone from 2 seconds toe minutes, while the furnace is maintained at atemperatureof from about 1'700 electrical resistivity of about 87'6 ohms/mil foot as drawnand solution-treated at1800 F. Upon aging for about? hours at 900 nae electrical resistivity of this ,alloy has been increased to 5.3 m. .m 1-fQ To further illustrate the alloys of thisinvention and the method of preparing them,. the .fol-( lowing detailed descriptions are presented by Way of example, it being understood that the inven tion is not to be considered as limited thereby.

Example I A magnesia-lined induction furnace was used in melting down 4.2 pounds of nickel and 0.022 pound of N10, the NiO being added to reduce the hydrogen content of the melt. When the nickel was molten, 2.1 pounds of electrolytic manganese was added. Before being added to the melt, the electrolytic manganese was treated to remove hydrogen, by being heated to about 1000 F. and then cooled slowly in a heat-treating furnace. 0.72 pound of chromium metal of the fused-chromium type containing less than 0.06% carbonand less than 1% iron was added. The heat was completely molten at 2610 F. at which time 0.042 pound of CaSi and 0.011 pound of Si metal were added. 0.01 pound of aluminum was then added and the heat was poured at 2810 F. into a -pound ingot mold and into a small bar mold which gave bars of A," and diameter. These small bars were cleaned up and swaged at 1800 F. to 0.125" diameter without diificulty. The 5-pound ingot was forged at 1825 F. to 1%" square. The 1 square stock was hot-rolled at 1800 F. to A diameter. The swaged and the hot-rolled material was wire-drawn to 0.070" diameter. In

the 0.070" diameter size as solution treated for 1 hours at 1800 F. the electrical resistivity was 869 ohms/mil foot. This was increased to 960 ohms/mil foot by aging for 48 hours at 700 F. A 72-hour aging at 700 F. produced an electrical resistivity of 990 ohms/mil foot and a96- hour aging at 700 F. increased the resistivity value to 1007 ohms/mil foot. The electrical resistivity of this alloy wiredrawn, and in the solution-treated state, has been increased from 876 ohms/mil foot to as much as 1052 ohms/mil foot by aging at 900 F. for three hours. The alloy composition was about 60% Ni, 10% Cr, and Mn.

Ewample 2 This alloy had an intended composition of 54.35% Ni, 18.1% Cr, 27.2% Mn, and 0.35% Si, and was prepared by first melting 4.2 pounds of electrolytic nickel and 0.022 pounds of MO in a magnesia-lined induction furnace. As soon as this material was melted, 2.1 pounds of electrolytic manganese, previously annealed to remove hydrogen, was added. 1.4 poundsof fusedchromium metal was added, and, when the melt was completely fluid, 0.042 pound of CaSi and 0.011 pound of silicon metal were stirred into the melt. At this time the temperature of the melt was 2620 F. When the melt had been heated to 2710 F., 0.010 pound of aluminum wire was plunged into the melt, and the melt poured immediately. The processing of this heat was exactly thesame as has been described in connection with Example I. The electrical resistivity after a solution-treatment at 1800 F. for 1 hours was 863 ohms/mil foot. This value was increased as follows by aging:

(a) After aging for 48 hours at 700 ohms/mil foot.

(b) After aging for 72 hours at 700 F.-889 ohms/mil foot.

(0) After aging for 96 hours at 700 F.--893 ohms/mil foot.

The above examples illustrate the efiect of the solution treatment followed by aging in improving the resistivity values of the alloys of this invention.

Temperature coefiicients oi. resistivity for these Ni-Cr-Mn alloys have been measured and, in general, values in the range from .000030 to +.000020 have been obtained. It seems reasonably certain that a value of +.00004 may be set as the maximum for the temperature coefficient of resistivity of these Ni-Cr-Mn alloys.

Small amounts of incidental elements will not prove detrimental to the beneficial results to be obtained in accordance with the present invention. For example, small amounts of iron or carbon may be present, while aluminum and silicon in contents up to 0.5% have been shown not to be detrimental.

In view of the above disclosure and description, it will now be apparent that new alloys for, and methods of preparing electrical resistor elements have been discovered, wherefore the novel features are hereinafter set forth in the attached claims.

What is claimed is:

1. An alloy for electrical resistor elements consisting of 50% to 70% Ni, 8% to 28% Cr, and the balance essentially all Mn, said Mn constituting 15% to 36% of the alloy, the resistivity properties of said alloy having been improved by solution treatment at 1500 F. to 2100 F. for from about 2 seconds to about hours followed by an aging treatment at a temperature of from 800 F. to 1200 F. for a period of from A; to 100 hours.

2. An alloy for electrical resistor elements consisting essentially of about 54.35% Ni, about 18.1% Cr, and about 27.2% Mn and which has been solution treated at 1700 F. to 2100 F. for from about 2 seconds to about 100 hours followed by an aging treatment at a temperature of from 850 F. to 950 F. for a period of from 1 to 5 hours.

3. An alloy for electrical resistor elements consisting of 50% to 70% Ni, 8% to 28% Cr, and the balance essentially all Mn, said Mn constituting 15% to 38% of the alloy, said alloy having been treated toimprove its resistivity properties by a strand anneal at a temperature in the range 1700 F. to 2100 F. and at a rate such that the wire is in the heating zone for from 2 seconds to 4 minutes, followed by an aging treatment at about 850 F. to 950 F. for a period of from 1 to 5 hours.

'by a strand anneal at a temperature in the range 1700 F. to 2100 and at a rate such that the wire is in the heating zone for from 2 seconds to 4 minutes, followed by an aging treatment at about 850 to 950 F. for a period of from 1 to 5 hours.

5. An electrical resistance alloy composed of 50% to 70% by weight nickel, 8% to 28% by weight chromium, and the balance essentially all manganese, said manganese constituting from 15% to 36% by weight of the alloy.

6..An electrical resistance alloy composed of 55% to 65% by weight nickel, 8% to 20% by weight chromium, and the balance essentially all manganese, said manganese constituting from 25% to 33% by weight of the alloy.

JOHN H. JACKSON. CHARLES T. GREENIDGE.

(References on following page) I Number REFERENCES CITED 2,242,970 The following references are of record in the 2,460,590 file of this patent: 2,497,667

UNITED STATES PATENTS 5 Number. Name Date Number 1,803,467 Driver May 5, 19 1 22,884/35 2,005,430 Lohr June 18, 1935 2,048,647 Feussner et a1 July 21, 1936 10 Name Date Fetz May 20, 1941 Lohr Feb. 1, 1949 Gresham et a1. Feb. 14, 1950 FOREIGN PATENTS Country Date Australia May 20, 1936 

1. AN ALLOY FOR ELECTRICAL RESISTOR ELEMENTS CONSISTING OF 50% TO 70% NI, 8% TO 28% CR, AND THE BALANCE ESSENTIALLY ALL MN, SAID MN, CONSTITUTING 15% TO 36% OF THE ALLOY, THE RESISTIVITY PROPERTIES OF SAID ALLOY HAVING BEEN IMPROVED BY SOLUTION TREATMENT AT 1500* F. TO 2100* F. FOR FROM ABOUT 2 SECONDS TO ABOUT 100 HOURS FOLLOWED BY AN AGING TREATMENT AT A TEMPERATURE OF FROM 600* F. TO 1200* F. FOR A PERIOD OF FROM 1/4 TO 100 HOURS. 